1. Field of the Invention
The present invention relates to inkjet-printing materials as recording mediums and coating agents therefor, more particularly a coating agent for inkjet-printing materials providing excellent reproducibility of colors and capable of forming thereon a definite, i.e., clearly defined and certain, image having a high resistance to weathering including a high resistance to water and light, and which is free of an irritating odor due to acetic acid. The present invention also relates to the inkjet-printed material made by using the coating agent and also free of the irritating odor.
2. Description of Related Art
Hitherto, as a base material for image-printing materials, there have been employed, for example, various materials made from papers, plastic, metals, glasses, ceramics, leathers and woods. Furthermore, these printed base materials are of various forms, i.e., may be various films, sheets, flat plates, articles having a curved surface or irregular surface, woven fabrics, non-woven fabrics and foams.
As inkjet-printing base materials used in an inkjet printer there have been generally employed materials having ink-receptive layers formed on the opposite sides thereof by applying thereto a treating agent containing a cationic polymer. The cationic polymer-containing treating agent should be capable of rapidly absorbing the water content of aqueous inks and firmly fixing printed inks on printing base materials, thus preventing the printing base materials treated with the treating agent from being stained with ink just after printing.
Nevertheless, however, the above-mentioned treating agent in the ink-receptive layer applied on the inkjet-printing base materials is highly soluble in water. Therefore, with the above-mentioned treating agent there is such a problem that the printed base materials become stained with ink when the images printed on the ink-receptive layers are brought into contact with water.
In order to solve this problem, some proposals have been made, i.e., it has been proposed that a porous material be added to the cationic polymer-containing treating agent applied to the printing base material forming the ink-receptive layer (see JP Patent Unexamined Application Nos. S60-245588A, H7-2430B and H3-275378A). Of these, JP S60-245588A discloses an inkjet-printing base material having at least one ink-receptive layer formed thereon, said ink-receptive layer containing a porous alumina xerogel having pores of 40 to 1,000 xc3x85 in radius. JP Patent Unexamined Application No. H7-2430B discloses a recording sheet comprising a transparent base having a porous ink-receptive layer formed thereon, said ink-receptive layer being mainly comprised of pseudo-boehmite and containing pores of 100 to 1,000 xc3x85 in radius, and the total volume of the pores in the layer being 0.1 cc/g or less.
The printing materials provided with the porous material-containing ink-receptive layers can absorb the water and solvent contents of the ink into the specified pores of the porous material. Thus, the printed materials can be prevented from being stained with the ink, thereby improving the quality, such as a color density and coloring property, of images.
However, with the printing materials provided with porous material-containing ink-receptive layers problems have often occurred due to the poor dispersibility of the porous material. That is, a coating liquid comprising the porous material and an adhesive is easily gelled, hard to apply uniformly onto the base of the printing material, the applied ink-receptive layers are easily cracked when dried, or eventually printed materials are easily stained with ink, not providing any definite images.
In order to solve these problems, JP Patent Unexamined Application No. H4-67985A proposes a coating agent comprising an alumina sol containing a monocarboxylic acid such as acetic acid and a water-soluble polymer binder added thereto, and a printing sheet comprising a polyethyleneterephthalate(PET) film having the coating agent applied thereon. However, the coating agent mentioned above has a problem of the monocarboxylic acid emitting an irritating odor. Furthermore, the printing sheet also has the same problem of emitting the irritating odor, which is uncomfortable and unpleasant to users.
In addition, JP Patent No. 2714350 proposes a printing base material provided thereon with an ink-receptive layer by a dispersion of an alumina hydrate containing 0.1 to 1.0 wt % of a nitrate group and having a pore radius distribution having maximal values within less than 100 xc3x85 and between 100 xc3x85 and 200 xc3x85. However, the nitrate group contained in the dispersion mentioned above is only an impurity of the alumina hydrate. Therefore, use of the dispersion mentioned above does not solve the problem of the printing material provided with the porous material-containing ink-receptive layer.
One object of the present invention is to provide a coating agent for producing an inkjet-printing material free of an irritating odor, which coating agent is good in dispersing alumina and applied to a base such as paper and plastic films.
Another object of the present invention is to provide an inkjet-printing material which is free of an irritating odor and good in reproducibility of colors, has a high resistance to water and weathering, and provides definite images thereon.
In accordance with the present invention, the coating agent is an alumina dispersion comprising alumina dispersed in an aqueous dispersing medium, aluminium nitrate and a binder. The present invention is different from the invention disclosed in said JP Patent 2714350 on the point of view that the coating agent in the present invention contains not alumina hydrate but alumina and aluminium nitrate and ink-receptive layer contains not alumina but alumina hydrate and not contains aluminium nitrate.
In a preferred embodiment of the coating agent of the present invention, the alumina is substantially xcex4-alumina having an average primary particle size of 5 to 100 nm, the amount of aluminium nitrate added is within the range of 0.1 to 10 parts by weight based on 100 parts by weight of alumina, particularly xcex4-alumina.
In accordance with the present invention, an ink-receptive layer is provided on the base material by applying the coating agent mentioned above onto the base to thereby produce the inkjet-printing material.
The coating agent of the present invention is described below.
Each of the alumina dispersion and the binder used in the coating agent of the present invention is described below.
The alumina dispersion comprises an aqueous dispersing medium containing alumina dispersed therein, and aluminium nitrate.
(1) Alumina
The alumina may be anhydrous aluminum oxide or hydrous aluminum oxide.
The anhydrous aluminum oxide may be xcex1-alumina, xcex2-alumina, xcex3-alumina xcex4-alumina, xcex8-alumina or "khgr"-alumina.
The hydrous aluminum oxide may be an alumina hydrate such as boehmite, pseudboemite, gibbsite, bayerite, norstrandite, diaspore, toedite, alumina gel, which may be called xe2x80x9caluminum hydroxidexe2x80x9d.
In the present invention, xe2x80x9caluminasxe2x80x9d includes xe2x80x9canhydrous aluminaxe2x80x9d and xe2x80x9calumina hydratesxe2x80x9d, if not specified.
Of the aluminas, for example, an alumina is preferably made by a vapor phase process, i.e., by hydrolyzing a gaseous metal chloride in the presence of water produced in the oxygen-hydrogen reaction at the temperature specific to the oxygen-hydrogen reaction, more specifically xcex4-alumina.
One or more of the alumina may be used in the coating agent of the present invention.
The alumina is desirably used in a powder form. The alumina particles in powdery form have an average primary particle size of preferably 5 to 100 nm, particularly preferably 5 to 50 nm. When the average primary particle size is in this range, the dispersion of the alumina is much better. The average primary particle size may be determined by an electron microscope.
The amount of the alumina added to the alumina dispersion is normally at most 60 wt %, preferably 15 to 50 wt %. When the amount is within this range, the alumina is more effectively dispersed. If the amount does not exceed 60 wt %, there occurs no unpreferred thickening or gelling due to shorter distances between alumina particles. When the amount of the alumina in the coating agent is not more than 60 wt %, particularly within the range of 15 to 50 wt %, the viscosity of the alumina dispersion can easily be adjusted to preferably a range of 50 to 1,000 cps. Thus, the coating agent of the present invention is easy to handle.
(2) Aqueous Dispersing Medium
The aqueous dispersing medium for dispersing the alumina maybe, for example, water, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, acetone, methylethyl ketone, ethyl acetate and/or glycols. A mixed medium comprising one or more of the aqueous dispersing mediums may be selected.
The mixed medium may be, for example, of water and isopropyl alcohol; water and methanol and/or ethanol; water, ethylene glycol and isopropyl alcohol; water, ethylene glycol, isopropyl alcohol and ethyl acetate.
(3) Aluminium Nitrate
A dispersant for the alumina dispersion may be aluminium nitrate. The aluminium nitrate is considered to assist the dispersion of alumina particles in the alumina dispersion and the coating agent of the present invention.
The aluminium nitrate may be, for example, aluminium nitrate nonahydrate, aluminium nitrate octahydrate, aluminium nitrate hexahydrate or aluminium nitrate tetrahydrate. Particularly, aluminium nitrate nonahydrate is preferred, because it is stabler than the others.
The amount of the aluminium nitrate added to the alumina dispersion is normally 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of alumina in the alumina dispersion. If the amount is less than 0.1 part by weight based on 100 parts by weight of alumina, no adequate thickening effect and high resistance to weathering can be obtained, that is the object of the present invention cannot be achieved. On the other hand, if the amount exceeds 10 parts by weight based on 100 parts by weight of alumina, then the viscosity of the alumina dispersion is too high, and the dispersion may sometimes become gelled.
In the alumina dispersion, to the aluminium nitrate may be added at least one of the other metal nitrates, such as magnesium nitrate, calcium nitrate, nickel nitrate and zinc nitrate. When the metal nitrates are used together with the aluminium nitrate, the amount thereof is not more than 10 parts by weight, preferably within the range of 0.1 to 10 parts by weight based on 100 parts by weight of aluminium nitrate for the purpose of producing a stable alumina dispersion.
(4) Process for Producing Alumina Dispersion
The alumina dispersion can be produced by mixing aluminium nitrate, alumina and an aqueous dispersing medium. This mixing may be carried out by a supersonic dispersing machine, sand mill, static mixer or high pressure dispersing machine, to uniformly disperse alumina into the aqueous dispersing medium.
In the present invention, the pH of the alumina dispersion may be regulated or adjusted to a weakly acidic range, preferably pH 2 to pH 6, so that the dispersion may be more effectively made.
(5) Other Components in the Alumina Dispersion
In order to regulate the pH of the alumina dispersion, one or more of inorganic acids, organic acids and nitrogen-containing carboxylic acids may be added to the alumina dispersion.
As the inorganic acid, reference may be made in general to inorganic acids such as nitric acid.
As the organic acid, reference may be made to a dicarboxylic acid, aromatic carboxylic acid, hydroxycarboxylic acid or nitrogen-containing carboxylic acid.
The dicarboxylic acid may be oxalic acid, malonic acid, succinic acid, maleic acid or fumaric acid.
The aromatic carboxylic acid may be benzoic acid or toluyl acid.
The hydroxycarboxylic acid may be glycolic acid, lactic acid, tartaric acid, malic acid or citric acid.
The nitrogen-containing carboxylic acid may be a carboxylic acid containing at least one nitrogen atom in the molecule thereof, such as amino acid or nicotinic acid.
If acetic acid or formic acid is added to the alumina dispersion, then an irritating odor may be emitted during the step of the production of the coating agent, i.e., the step of mixing the alumina dispersion and the binder liquid mentioned below, and during the step of the production of the inkjet-printing material, i.e., the step of applying the coating agent to the printing base material. The obtained inkjet-printing material may also have an irritating odor derived from the acetic acid, etc. Therefore, acetic acid and formic acid should be used in as small an amount as possible, in the alumina dispersion, if they can or must be present in the it.
(6) Amount of Alumina Dispersion in the Coating Agent
The amount of the alumina dispersion in the coating agent is normally not less than 15 wt %, preferably 15 to 50 wt %. When the amount of the alumina dispersion is within the range above, the object of the present invention can be adequately achieved, and since an adequate thickness can be obtained by one application step, a single layer coating can achieve the ink-receptive layer required by the present invention. Therefore, the inkjet-printing material can be produced at low cost.
The binder to be added to the coating agent of the present invention may be an organic polymeric substance such as starch or, any of its modified products, polyvinyl alcohol or any of its modified products, a soluble polyamide soluble in a solvent such as an alcohol, hydroxycellulose, hydroxymethyl cellulose, carboxymethyl cellulose or polyvinyl pyrrolidone. Furthermore, at least one of SBR latex and NBR latex may be added as an adjuvant for improving the adhesion between the ink-receptive layer and the base.
Of the organic polymeric substances, polyvinyl alcohol and its modified products and soluble polyamide are preferred. Particularly, a mixture of polyvinyl alcohol with one of the modified products of polyvinyl alcohol, i.e., polyvinyl acetal, is preferred.
Polyvinyl acetal having a molecular weight of 10xc3x97104 to 20xc3x97104 and a degree of acetallization of 0.3 to 10 mol % is particularly preferred. If the molecular weight and degree of acetallization of the polyvinyl acetal are within the above-mentioned ranges, then the obtained coating agent is not gelled. Therefore, a high quality inkjet-printing material can easily be obtained by applying the coating agent to the base. The obtained ink-receptive layer has an adequate thickness and a high resistance to water. Thus, the images formed on the ink-receptive layer are highly definite and does not flow with water.
Of the polyvinyl alcohols mentioned above, one having a saponification value of 65 to 90 mol % is preferred. If the saponification value of the polyvinyl alcohol is within the above-mentioned range, then the obtained ink-receptive layer is good both in its resistance to water and ink-absorbing rate.
The binder, particularly polyvinyl alcohol and polyvinyl acetal may be used in an aqueous solution or an alcoholic solvent solution.
As the alcoholic solvent reference may be made to a lower aliphatic alcohol, glycol, or a mixed solvent of another solvent with the lower apliphatic alcohol.
The lower aliphatic alcohol may be, for example, methanol, ethanol, propanol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, etc.
The glycol may be, for example, ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 2-ethyl-1,3-hexanediol, etc.
As the mixed solvent mentioned above, reference may be made to mixtures of at least one solvent of water, benzyl alcohol, formic acid and acetic acid with the above-mentioned lower aliphatic alcohol. More specifically, the mixed solvent is a mixture of water and methanol.
The amount of the binder added to the coating agent of the present invention varies depending on the layer thickness required. It is normally 5/1 to 12/1 in terms of the alumina/binder (solid weight ratio), preferably 5/1 to 10/1.
If the amount of the binder is below the above-mentioned range, then the adhesion between the ink-receptive layer and the base is lowered to an extent that it cannot be practically used.
On the other hand, if the amount of the binder is beyond the range mentioned above, then the obtained inkjet-printing material may have so poor an ink-absorbing power that the ink-fixing power is lowered.
To the coating agent of the present invention may be further added a leveling agent.
This leveling agent may be, for example, a water-soluble modified silicone oil and a water-soluble fluorine-containing surface active agent.
The water-soluble modified silicone oil may be, for example, an alcohol-modified silicone oil and an ether-modified silicone oil.
The water-soluble fluorine-containing surface active agent may be, for example, a perfluoroalkyl sulfonate, perfluoroalkyl carboxylate and perfluoroalkyl betaine.
To the coating agent of the present invention may be added such amounts of some further additives that they are not a bar against the objects of the present invention. These additives may be a pH-regulating agent, viscosity-regulating agent, antifoaming agent, defoaming agent, dispersion-stabilizing agent, brightening agent and releasing agent, etc.
The process for preparing the coating agent of the present invention is not specifically limited. The coating agent of the present invention may be prepared by, for example, firstly preparing both the above-mentioned alumina dispersion and a binder liquid containing the above-mentioned binder dissolved or dispersed in water or the above-mentioned alcoholic solvent and then mixing the alumina dispersion and the binder liquid; firstly preparing the alumina dispersion and then dissolving or dispersing a binder in the alumina dispersion; or mixing together all the alumina, aluminium nitrate and aqueous dispersing medium, which are the main ingredients of the alumina dispersion, the binder and, if necessary, the solvent for the binder.
In any of the processes mentioned above, a more uniform dispersion may be obtained by using an apparatus such as a supersonic dispersing machine, sand mill, static mixer or high pressure dispersing machine in any step of the process. For example, such an apparatus may be used in a step of mixing the alumina dispersion and the binder liquid; in a step of dissolving or dispersing the binder into the alumina dispersion; or mixing together all the ingredients, alumina, aluminium nitrate, aqueous dispersing medium, binder and dispersing medium.
The coating agent obtained by any of the processes mentioned above is preferably defoamed by a supersonic defoaming or vacuum defoaming treatment.
The inkjet-printing material of the present invention comprises the ink-receptive layer formed from the coating agent mentioned above and the base supporting the ink-receptive layer.
In the inkjet-printing material of the present invention, the ink-receptive layer has the function of receiving an ink jetted from an inkjet printer to the inkjet-printing material to form an image on the material.
The thickness of the ink-receptive layer is not limited, but is normally 10 to 60 xcexcm, practically preferably 20 to 50 xcexcm.
The shape of the base is not specified. The base may be a film, sheet, flat plate, an article having a curved surface or irregular surface, a woven fabric, non-woven fabric or foam.
The base may be made from papers, fabrics, plastic films, foamed sheets, glass sheets, ceramic sheets, leather sheets, and metal sheets or foils. These base materials may be used singly or in combination, e.g., in a laminated form of two or more of these materials.
The papers above may be fine quality papers, handmade papers, Japanese paper and printing papers.
The fabrics above may be woven fabrics and non-woven fabrics.
The plastic films above may be made of a polymer such as polyethylene terephthalate.
The foamed sheets above may be a foamed polystyrene sheet, foamed polyethylene sheet, and foamed polypropylene sheet.
The metal sheets or foils above may be a stainless sheet or foil, aluminum sheet or foil, iron sheet or foil, and steel sheet or foil.
In the present invention, the above-mentioned coating agent is coated on the base to form the ink-receptive layer.
The coating operation may be carried out by using any of a blade coater, reverse coater, die coater, comma coater, or air knife. In addition, the coating may be carried out by a gas-jetted aerosol spraying, or a manual pumping spraying, or further by brush coating, spatula coating or rod coating. The ink-receptive layer having an even thickness can be obtained on the base by any of the coating methods mentioned above.
The coating agent may be coated directly or via a primer on the base.
In the coating agent of the present invention, the alumina dispersion contains aluminium nitrate. This makes it possible to avoid the disadvantages, such as thickening of aqueous dispersing mediums, agglomeration and precipitation of alumina or gelling of the alumina dispersion, which are observed in the prior art alumina dispersions.
In the inkjet-printing materials, an ink component such as a dye is fixed on the alumina of the ink-receptive layer when printed. The coating agent of the present invention contains alumina uniformly dispersed therein. Therefore, the ink-receptive layer made from the coating agent also contains the alumina uniformly deposited therein. Accordingly, the ink component is not unevenly fixed in the ink-receptive layer of the inkjet-printing material according to the present invention.
In some inkjet-printing procedures, an anionic ink component contained in the inkjet-printing ink and the alumina contained in the ink-receptive layer of the inkjet-printing material of the present invention attract each other through an electrical force. This improves the ink-fixing effect.
According to the present invention, the particles of the alumina contained in the ink-receptive layer have an average primary particle size ranging from 5 to 100 nm. Therefore, the ink component is rapidly and evenly fixed in the ink-receptive layer. On the other hand, the water or organic solvent contained in the ink is rapidly and evenly diffused into the ink-receptive layer. Therefore, the inkjet-printing material of the present invention can provide a more rapid set which is dry to the touch, so that higher quality images can be obtained.
Using the inkjet-printing material of the present invention realizes images of a high image quality, clear color, high color density and high water resistance, and firmly fixed on the material.